Both my Janomes notify me when bobbin is getting low, but my favorite thing is my Janome MC11000se has a separate built-in bobbin winder on top of the machine. That means I don't have to un-thread anything to rewind a bobbin. It's great! Great little invention.
I did own an individual bobbin winder (one of the hot sale items a few years ago) but that didn't work as well as I wanted... kept skipping across table when in use and in the end the thread wasn't evenly wound. So once I got my MC11000se I gave the bobbin winder to a friend who desperately wanted one along with all my warnings about it dancing across the table. Her husband built a special clamp to hold it down and she's happy with it.